Overview
Definition:
Fistulotomy is a surgical procedure used to treat anal fistulas by opening the fistula tract and allowing it to heal as a superficial wound
It is primarily indicated for low anal fistulas, typically those originating from the Goodsall's rule, where the internal opening is located in the posterior midline and the external opening is within 3 cm of the anal verge.
Epidemiology:
Anal fistulas affect approximately 1-3% of the population, with men being more commonly affected than women
Low anal fistulas (transsphincteric and intersphincteric, less than 30% of the external anal sphincter) constitute a significant proportion of these cases
They are often secondary to an anal gland infection or abscess.
Clinical Significance:
Untreated anal fistulas can lead to chronic pain, recurrent abscesses, incontinence, and social embarrassment
Fistulotomy offers a definitive solution for low anal fistulas with a high success rate, preserving anal sphincter function when performed correctly, which is crucial for patient quality of life and surgical resident training.
Clinical Presentation
Symptoms:
Persistent purulent or fecal discharge from an opening in the perianal skin
Intermittent pain, especially with bowel movements, if the tract becomes partially occluded
A palpable tender lump or swelling around the anus
Bleeding from the external opening
Recurrent anal abscesses and drainage.
Signs:
A visible external opening on the perianal skin, often with granulation tissue or induration around it
Digital rectal examination may reveal a palpable cord-like tract connecting the external opening to the anal canal
Tenderness over the fistula tract
Signs of local inflammation or infection.
Diagnostic Criteria:
Diagnosis is typically based on a thorough history and physical examination
The presence of an external opening with associated discharge, coupled with findings on digital rectal examination suggestive of an internal opening, is sufficient for diagnosing a simple low anal fistula
Imaging is usually reserved for complex or recurrent fistulas.
Diagnostic Approach
History Taking:
Inquire about the duration and nature of discharge (purulent, bloody, fecal)
Ask about any history of anal abscess, trauma, inflammatory bowel disease (Crohn's disease), or previous anorectal surgery
Note any associated pain, fever, or changes in bowel habits
Assess for any symptoms of fecal incontinence.
Physical Examination:
Perform a careful perianal inspection to identify the external opening, noting its location and any surrounding inflammation or induration
Perform a digital rectal examination to assess for tenderness, induration, and the presence of an internal opening
Gently probe the external opening to assess the direction and depth of the tract, if possible without causing significant pain
Consider a high-lithotomy position for better visualization.
Investigations:
For simple low anal fistulas, further investigations are often unnecessary
However, for complex or recurrent fistulas, or if inflammatory bowel disease is suspected: Magnetic Resonance Imaging (MRI) of the pelvis is the gold standard for mapping fistula tracts and identifying internal openings and abscesses
Endoscopic ultrasound (EUS) can also be useful
Anoscopy or rigid sigmoidoscopy may help visualize the internal opening in select cases.
Differential Diagnosis:
Perianal abscess, hidradenitis suppurativa, pilonidal sinus, anal fissure with secondary infection, and tuberculosis of the anus
In cases of suspected Crohn's disease, other extra-intestinal manifestations should be sought.
Management
Initial Management:
For symptomatic low anal fistulas without abscess, fistulotomy is the definitive treatment
If an abscess is present, incision and drainage of the abscess is the priority before definitive fistula treatment
Patients should receive adequate analgesia and wound care instructions.
Medical Management:
Antibiotics are generally not indicated for uncomplicated anal fistulas unless there is significant surrounding cellulitis or abscess
Prophylactic antibiotics may be considered in immunocompromised patients or those with significant comorbidities
Management of underlying conditions like Crohn's disease is essential.
Surgical Management:
Fistulotomy is the primary surgical treatment for low anal fistulas
The goal is to incise the entire length of the fistula tract from the internal to the external opening, laying it open to granulate
This involves identifying the fistula tract using a probe or by following the discharge
The tract is then incised, including the overlying skin, subcutaneous tissue, and the internal and external sphincters if they are within the tract
Careful hemostasis is achieved
Postoperative care focuses on wound hygiene and preventing premature closure.
Supportive Care:
Postoperative care includes regular sitz baths (warm water soaks) to promote healing and hygiene, pain management with analgesics, and stool softeners to prevent straining
Patients are educated on wound care and to expect some drainage and discomfort for several weeks
Follow-up appointments are crucial to monitor healing and assess for complications.
Complications
Early Complications:
Bleeding, pain, infection of the wound, urinary retention, temporary fecal incontinence
Sepsis can occur if an abscess is missed or inadequately drained.
Late Complications:
Fistula recurrence (due to incomplete treatment or missed internal opening), anal stricture, chronic wound, permanent fecal incontinence (more common with high fistulas or extensive sphincter division).
Prevention Strategies:
Accurate identification of the internal opening is paramount
Complete division of the fistula tract without sacrificing excessive sphincter muscle is key
Careful postoperative wound care to prevent premature closure and promote healthy granulation
Appropriate patient selection and counseling regarding potential risks, especially incontinence.
Prognosis
Factors Affecting Prognosis:
The success rate of fistulotomy for low anal fistulas is high, typically 90-95%
Factors influencing prognosis include the accurate identification of the internal opening, the patient's overall health, the absence of underlying conditions like Crohn's disease, and proper surgical technique
Recurrence is more likely with complex or high fistulas.
Outcomes:
Most patients experience complete healing of the fistula within 6-8 weeks with minimal long-term sequelae
The risk of significant anal incontinence is low for well-selected low anal fistulas treated with fistulotomy
The main concern is recurrence.
Follow Up:
Regular follow-up appointments are recommended at 2-4 weeks post-operatively and then as needed, to monitor wound healing, assess for signs of recurrence, and address any complications
Long-term follow-up may be required for patients with associated medical conditions.
Key Points
Exam Focus:
Fistulotomy is for low anal fistulas
simple transsphincteric or intersphincteric less than 30% of sphincter
Identify internal opening accurately
Lay open the entire tract
Risk of incontinence increases with sphincter division.
Clinical Pearls:
Goodsall's rule is crucial for predicting internal opening location in low posterior fistulas
Always rule out underlying Crohn's disease or other inflammatory conditions
Ensure adequate pain control and wound hygiene postoperatively.
Common Mistakes:
Treating a high fistula with fistulotomy, leading to high incontinence risk
Incomplete division of the fistula tract, leading to recurrence
Premature closure of the external wound, causing abscess formation
Misidentifying the internal opening or missing associated abscesses.